Horsham Stone is a type of calcerous, flaggy sandstone containing millions of minute sand grains and occurring naturally in the Wealden clay of the English county of West Sussex. It is also high in mica and quartz. The rock extends in an arc-like formation for several kilometres around the town of Horsham from which it takes its name, and lies just below the Wealden clay surface in bands 4 to 5 inches (10 to 13 cm) thick. Horsham Stone is famous for its ripple-marked appearance, formed by the action of the sea similar to the ripples on the sandbanks and beaches of Sussex.